drm/i915/tc: Don't connect the PHY in intel_tc_port_connected()

Connecting the PHY for connector probing - also blocking TC-cold - isn't
required and has some overhead. Taking only the mutex is sufficient, so
do that.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323142035.1432621-25-imre.deak@intel.com